DRY HYDROGEN PRODUCTION IN A TANDEM WATER PHOTOELECTROLYSIS CELL

The existence of several concerns related to the increasing energy demand and the related environmental crisis indicates the need to identify innovative, effective and low-cost solutions. Photoelectrochemical water splitting is recognized as a promising strategy and it attracts particular interest for storing solar energy into the chemical bonds of hydrogen as fuel. Since overall water splitting consists of two half-reactions, i.e., water oxidation to oxygen and reduction to hydrogen, it is natural to use a two-photoelectrode configuration to maximize both processes with the cell illuminated from the higher energy gap semiconductor. The longer wavelength photons that are not absorbed by the top large band gap absorber are transmitted to and harvested by the bottom low band gap absorber. Owing to band bending, the photogenerated electrons in p-type photocathodes and holes in n-type photoanodes migrate toward the semiconductor-electrolyte interface to reduce and oxidize water, respectively. In parallel, photogenerated holes in the photocathode and electrons in the photoanode are transferred to the external circuit and recombine at the Ohmic back-contact that connects both photoelectrodes. Therefore, a PEC tandem device can achieve potentially higher efficiency than a single absorber system, with large solar spectral coverage and a wide window of suitable materials to choose. However, no materials and cell configurations fully satisfy so far, all the stringent requirements for practical application, including appropriate stability, straightforward separation of the produced gases, gas dryness, low-cost characteristics and scalable module manufacturing. All these aspects still make the design of the PEC system quite challenging and indicate the need to address towards novel solutions. This work addresses for the first time the use of a porous hydrophobic backing layer in a PEC cell to allow production of dry hydrogen and increase system simplicity.